The Federal Vacancies Reform act stipulates that an acting official must be the agency’s top deputy, another Senate-confirmed official or a senior agency official who had been in their job for at least 90 days prior to a vacancy.

Nadler, Thompson and Cummings requested that the Department of Homeland Security provide "a detailed explanation of the legal basis for his appointment" as well as certain documents and a briefing on the matter.

"It appears the Administration was aware that Mr. Cuccinelli could not be appointed Acting Director of USCIS consistent with the Federal Vacancies Reform Act," they wrote.

The Hill has reached out to the White House, Department of Homeland Security and USCIS for comment.

At the time of Cuccinelli's appointment earlier this month, A Department of Homeland Security spokesperson said “Mr. Cuccinelli’s appointment is in accordance with the Federal Vacancies Reform Act,” but did not elaborate.